We’re often told to rest when we’re sick. But studies have shown that regular exercise can actually be beneficial for people living with many diseases, including cancer.

“Exercise offers the cancer survivor a significant opportunity to be a key player in their healing team,” says Linda Gottlieb, research associate at the Yale School of Public Health and an American College of Sports Medicine-certified cancer exercise trainer based in Milford, Conn. “Exercise has also been proven to help decrease the chance of recurrence, along with improving quality of life.”

The ACME’s exercise guidelines for cancer survivors suggest avoiding inactivity and aiming for 150 minutes a week of moderate aerobic exercise and two to three days a week of strength training.

“Improved physical fitness is encouraged to buoy feelings of confidence, promote general feelings of well-being, decrease anxiety, depression and fatigue,” says Ms. Gottlieb. Research also supports exercising before undergoing surgery and during chemo and radiation treatment, she says.

Previously sedentary people should start conservatively. “For a non-exerciser survivor, being able to walk up the stairs without the fear of falling or being out of breath is a huge accomplishment,” she says.

Ardent exercisers should try not to think back to “when I didn’t have cancer.” “Your body has gone through a lot,” she says. “You need to be respectful, as sometimes more exercise can be counterproductive.” Ms. Gottlieb suggests working with a certified cancer exercise trainer or physical therapist who can help assess individual needs and limitations and create an appropriate and safe exercise prescription.